Keep visible process state if process embeds visible activity

The top activity in a embedded task may be a different process
than the organizer process, and the top activity can occlude
all activities belong to the organizer process. Then there is
no visible activities in the organizer process, which may cause
the organizer process to be frozen due to the background state.

Then when bringing the embedded task from background to front,
the organizer process may be unable to respose for
TaskFragmentOrganizerController#onTransactionHandled which is
used for synchronization of animation. Then it will lead to a
5s timeout.

Fix: 274017425
Test: atest TaskFragmentOrganizerControllerTest#
      testOnActivityReparentedToTask_activityNotInOrganizerProcess \
      _useTemporaryToken

Change-Id: I57ef9ebe95e05842e7f325c1a4775e98c7eb57bd